The present invention relates generally to aircraft engine fuel systems, and more particularly relates to ecology valves and systems of aircraft engine fuel systems.
Ecology systems are used in aircraft fuel systems to reduce nozzle coking, reduce pollution, and prevent fuel draining into the combustion chamber (and thereby prevent clouds of smoke upon starting). Ecology systems work by purging excess fuel remaining in the fuel manifold upon engine shut down. Upon engine shut down, the ecology valve draws or sucks excess fuel into a temporary sump chamber under mechanical action of a spring. While the engine is not operating, the fuel is stored in the sump chamber. Upon the next engine start up, the stored fuel is returned to the fuel manifold under the actuation force of pressurized fuel provided by the fuel pump. Ecology valves that operate according to the above manner are disclosed in U.S. Pat. Nos. 5,809,771 to Wernberg and 6,195,978 to Futa, Jr., the entire disclosures of which are hereby incorporated by reference.
Current ecology valve technology requires a return of working fuel used for ecology valve actuation to the fuel tank or other upstream location. While this is not problematic in new aircraft engines and fuel systems, and retrofits for existing fuel systems that have a readily available fuel tank drainage line, it is problematic for existing aircraft fuel systems that do not have an available fuel tank drainage line. Adding drain lines to existing systems to prevent nozzle coking is undesirable because of the additional cost and weight.
In light of the above, it is a general objective of the present invention to eliminate or reduce the return lines to the fuel tank or other upstream locations for ecology systems of aircraft fuel systems.
In accordance with these and other objectives, the present invention is directed toward an ecology valve that drains working fuel to the sump chamber of the ecology valve upon engine shut down. The ecology valve has a piston slidable in the piston chamber between shut-off and run positions. The piston divides the piston chamber into a sump chamber and an actuation chamber. Upon engine shut down, the piston slides toward the shut-off position and suctions sufficient fuel from the fuel manifold into the sump chamber to prevent coking of the nozzles. Upon the next engine start up, the actuation chamber is pressurized which drives the piston toward the run position and returns fuel contained in sump chamber to the fuel manifold. A drain passageway opens and fluidically connects the actuation chamber to sump chamber when the piston is sliding toward the shut-off position which allows fuel contained in the actuation chamber to drain to the sump chamber.
It is an aspect of the present invention that a novel mode switching valve is provided that communicates pumped fuel to the nozzles when the engine is running and blocks fuel flow when the engine is not operating. The mode switching valve blocks the drain passageway when the actuation chamber is filling with working fuel to allow fluid actuation of the ecology valve.
Other objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.